Low-frequency amplifier circuits



March 11, 1947. s, A, DlKSTAAL 2,417296 LOW-FREQUENCY AMPLIFIER G IRCUITS Filed March 23, 1943 ATTORNEY Patented Mar. 11, 1947 2,417,296 LOW-FREQUENCY AMPLIFIER CIRCUITS Simon Anne Dikstaal, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 23, 1943,

In the Netherlands April 9,

Ciaims. 1

This invention relates to a low-frequency amplifier circuit in which the oscillations to be amplified are fed to the grid circuit of an amplifier valve whose anode circuit includes the series connection formed by a condenser and the primary winding of a transformer from whose secondary winding the amplified oscillations are derived and whose anode direct voltage is supplied to the anode through a choke coil.

Such circuit is known to offer the advantage that the anode direct current of the amplifier valve does not pass through the primary winding of the transformer and that substantially higher values of the inductances of the windings can thus be achieved, as is desirable with a view of obtaining uniform amplification, even of the low frequencies.

In contradistinction to this advantage, the circuit has, however, the disadvantage that two iron cores (which are to be sufficiently free from iron losses and for this reason are to be formed from thin sheets of magnetic material), are needed, one for the choke coil and another for the transformer. This involves a. higher cost for assembling the iron cores. In addition, the choke coil and the transformer have to be mounted each individually and this further adds to the cost of the circuit. Since in practice, and more particularly in mass production, the cost of production should be kept as low as possible, the circuit described not well adapted for practical use.

According to the invention, a considerable saving in cost is achieved in the circuit described in that the choke coil winding and the two transformer windings are arranged respectively on the outer limbs of an iron core of the shell-type. This saving is achieved due to the fact that in a device according to the invention only one core need be stacked for the choke coil and the transformer jointly, any further treatment, such as impregnation or the like, needs only to be carried out for a sin le component member instead of two and. finally only one component member need be mounted in the apparatus.

In order that the invention may be clearly understood and readily carried into effect one form of construction of an amplifier circuit according to the invention is shown diagrammaticalliy i1 1. Figs. 2 and 3 show respectively front and end views of the iron core utilized in Fig. 1.

The amplifier circuit shown in. Fig. 1 includes amp Tier valve i which has the oscillations to he amplifie e. fed to it between the control grid 2 and the cathode 3. The amplified oscilla- Serial No. 480,189

tions occurring in the anode circuit of the valve I are fed to the small speech coil 4 of a dynamic loudspeaker 5. In series with the primary windillg of the output transformer 5 is connected a condenser 8 which prevents the anode direct current of the valve 5 from flowing through the primary winding of the transformer. The anode voltage is supplied to the anode l of the amplifier valve 2 with the interposition of a choke coil 9. The speech coil t is connected to the secondary winding of the transformer 8. The windings of the transformer 6 and of the choke coil 9 are arranged on the outer limbs l0 and I! respectively of an iron core E2 of the shell type which is formed from E-shaped and I-shaped transformer laminations of the kind use for shelltype transformers, shown respectively at it and it in Figs. 2 and 3. Due to the larger iron section of the middle limb 13 the magnetic lines of force of the choke coil Will not bring about saturation in the magnetic circuit of the transformer so that the primary inductance of the transformer is not affected by the anode direct current of the valve i which passes through the choke coil.

The condenser 8 is preferably so dimensioned that resonance occurs for any frequency in the lower-most part of the audible spectrum.

In the construction of the choke coil transformer combination the E- and I-shaped laminations may first be stacked at the correct level, the previously finished coils are then pushed each over one of the outermost limbs and after that the aggregate of choke coil and transformer can further be finished as a Whole, be impregnated and be subsequently housed in the set concerned.

What I claim is:

l. A low-frequency amplifier circuit in which the oscillations to be amplified are fed to the grid circuit of an amplifier valve and in which the anode circuit of the said valve includes the series combination of a condenser and the primary winding of a transformer from whose secondary winding the amplified oscillations are derived and in which the anode direct voltage is supplied to the anode of the valve through a choke ccii, wherein the choke coil winding and the two windings of the transformer are arranged respectively on the two outer limbs of an iron core of the shell type which is formed from E-shaped and I-shaped laminations, the central limb being so dimensioned with respect to the outer limbs that the magnetic lines of force due to the choke coil winding are ineiiective to bring about saturation in the magnetic circuit of the transformer, 0 that the primary inductance of the transformer is not affected by the anode direct current of the valve which passes through the choke coil winding.

2. An amplifier circuit as claimed in claim 1, wherein the condenser is so dimensioned that with the inductances present in the device resonance occurs'at any frequency in the lowermost part of the audible spectrum.

3. A low-frequency amplifier circuit in which the oscillations to be amplified are fed to the grid circuit of an amplifier valve and in which the anode circuit of the said valve includes the series combination of a condenser 'and'a transformer from which the amplified oscillations are derived and in which the anode direct voltagev is supplied to the anode of the valve through a choke coil, wherein the choke coil and the transformer are arranged respectively on the two outer limbs of an iron core of the shell type which is formed from E-shaped and I-shaped laminations, the centrallimbbeing so dimensioned with respect to the outer limbs that the magnetic lines of force due to the choke coil winding are ineffective'to bring about saturation in the magnetic circuit of the transformer, so that the primary inductance of the transformer is not affected by the anode .direct current of the valve which passes through the choke coil winding.

4. An audio frequency coupling system for coupling the output or anode of a vacuum tube amplifier to a utilization device, comprising a closed.

iron core having a central limb and two outer limbs, a choke coil through which direct voltage is supplied to the anode of the amplifier Wound around one of the outer limbs, a transformer having its primary winding connected to the amplifier anode and its secondary. winding connected to the utilization device, said transformer windings being wound around the second outer limb, the central limb being so dimensioned with respect to the outer limbs that the magnetic lines of force due to the choke coil winding are ini 4 effective to bring about saturation in the magnetic circuit of the transformer, so that the primary inductance of the transformer is not affected by the anode direct current of said amplifier which passes through the choke coil windmg.

5. An audio frequency coupling system for coupling the anode circuit of a vacuum tube amplifier to the voice coil of an acoustical reproducer, comprising a closed iron core having a central limb and two outer limbs, a choke coil through which direct voltage is supplied to the anode of said amplifier wound around one of the outer limbs, a transformer having its primary winding connected in series with a capacitor to the anode of said amplifier and its secondary winding connected to the voice coil of said reproducer, said transformer windings being wound around the second outer limb, and the center limb being so dimensioned with respect to the outer limbs that the magnetic lines of force due to the choke coil windings are ineffective to bring about saturation in the magnetic circuit of the transformer so that the primary inductance of the transformer is not affected by the anode direct current of said amplifier which passes through the choke coil winding, and said capacitor being of such value that with the inductances present in the system resonance occurs at any frequency in the lowermost part of the audible spectrum.

SIMON ANNE DIKSTAAL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,808,726 Donle June 2, 1931 1,908,934 Trube May 16, 1933 1,429,634 Robinson Sept. 19, 1922 1,881,515 Grimley Oct. 11, 1932 1,815,023 Donle July 14-, 1931. 

